ldiopathic inflammatory myopathy (poly/dermatomyositis) is an inflammatory disease of muscle in which characteristic autoantibodies occur. By applying a broad range of immunological, clinical, and epidemiological observations to a large (about 150) group of patients, we have developed evidence for subsets of patients which strongly suggest that the disease can be divided into more meaningful groups with different etiology and pathogenesis. So far, the groups of patients with anti-Jo-l antibodies and with antibodies to signal recognition peptide are clinically and epidemiologically as well as serologically distinct from each other and from other patients.